Introduced a new function non_nullable to BE, which can extract concrete data column from a nullable column. If the input argument is already not a nullable column, raise an error.
When the argument of truncate function is float type, it can match both truncate(DECIMALV3) and truncate(DOUBLE), if the match is truncate(DECIMALV3), the precision is lost when converting float to DECIMALV3(38, 0).
Here I modify it to match truncate(DOUBLE) for now, maybe we still need to solve the problem of losing precision when converting float to DECIMALV3.
This pr mainly to optimize the histogram(👉🏻https://github.com/apache/doris/pull/14910) aggregation function. Including the following:
1. Support input parameters `sample_rate` and `max_bucket_num`
2. Add UT and regression test
3. Add documentation
4. Optimize function implementation logic
Parameter description：
- `sample_rate`：Optional. The proportion of sample data used to generate the histogram. The default is 0.2.
- `max_bucket_num`：Optional. Limit the number of histogram buckets. The default value is 128.
---
Example：
```
MySQL [test]> SELECT histogram(c_float) FROM histogram_test;
+-------------------------------------------------------------------------------------------------------------------------------------+
| histogram(`c_float`) |
+-------------------------------------------------------------------------------------------------------------------------------------+
| {"sample_rate":0.2,"max_bucket_num":128,"bucket_num":3,"buckets":[{"lower":"0.1","upper":"0.1","count":1,"pre_sum":0,"ndv":1},...]} |
+-------------------------------------------------------------------------------------------------------------------------------------+
MySQL [test]> SELECT histogram(c_string, 0.5, 2) FROM histogram_test;
+-------------------------------------------------------------------------------------------------------------------------------------+
| histogram(`c_string`) |
+-------------------------------------------------------------------------------------------------------------------------------------+
| {"sample_rate":0.5,"max_bucket_num":2,"bucket_num":2,"buckets":[{"lower":"str1","upper":"str7","count":4,"pre_sum":0,"ndv":3},...]} |
+-------------------------------------------------------------------------------------------------------------------------------------+
```
Query result description：
```
{
"sample_rate": 0.2,
"max_bucket_num": 128,
"bucket_num": 3,
"buckets": [
{
"lower": "0.1",
"upper": "0.2",
"count": 2,
"pre_sum": 0,
"ndv": 2
},
{
"lower": "0.8",
"upper": "0.9",
"count": 2,
"pre_sum": 2,
"ndv": 2
},
{
"lower": "1.0",
"upper": "1.0",
"count": 2,
"pre_sum": 4,
"ndv": 1
}
]
}
```
Field description：
- sample_rate：Rate of sampling
- max_bucket_num：Limit the maximum number of buckets
- bucket_num：The actual number of buckets
- buckets：All buckets
- lower：Upper bound of the bucket
- upper：Lower bound of the bucket
- count：The number of elements contained in the bucket
- pre_sum：The total number of elements in the front bucket
- ndv：The number of different values in the bucket
> Total number of histogram elements = number of elements in the last bucket(count) + total number of elements in the previous bucket(pre_sum).
MySQL [db]> SELECT SUM(a.r[1]) as active_user_num, SUM(a.r[2]) as active_user_num_1day, SUM(a.r[3]) as active_user_num_3day, SUM(a.r[4]) as active_user_num_7day FROM ( SELECT user_id, retention( day = '2022-11-01', day = '2022-11-02', day = '2022-11-04', day = '2022-11-07') as r FROM login_event WHERE (day >= '2022-11-01') AND (day <= '2022-11-21') GROUP BY user_id ) a;
ERROR 1105 (HY000): errCode = 2, detailMessage = sum requires a numeric parameter: sum(%element_extract%(a.r, 1))
in the previous, the result is:
```
mysql> select array_position([1, null], null);
+--------------------------------------+
| array_position(ARRAY(1, NULL), NULL) |
+--------------------------------------+
| NULL |
+--------------------------------------+
1 row in set (0.02 sec)
```
but after this commit, the result become:
```
mysql> select array_position([1, null], null);
+--------------------------------------+
| array_position(ARRAY(1, NULL), NULL) |
+--------------------------------------+
| 2 |
+--------------------------------------+
1 row in set (0.02 sec)
```
